JPH0214796B2 - - Google Patents

Abstract

A layer of zirconium (44) can be used as an adhesion layer between a ceramic or polyimide substrate (40) and subsequently applied metallic layers (46,48,50). Following the zirconium layer, copper can be deposited (46) followed by a reaction barrier layer (48) and a wettable surface layer (50) such as gold. This type of structure can be used for pin brazing, chip joining, and/or wire connections.

Description

DETAILED DESCRIPTION OF THE INVENTION A. INDUSTRIAL APPLICATION The present invention relates to the use of zirconium in multilayer thin film metal structures. More particularly, it relates to the use of zirconium as an adhesive layer between ceramic or polyimide structures and copper or aluminum layers.

B. Prior art As integrated circuit density increases towards VLSI,
Increasing input/output (I/O) lines and interconnect densities have placed stringent demands on multilayer chip packaging technology. each with high I/O
To interconnect large numbers of integrated circuit (IC) chips with high terminal densities, the ability to form fine, precise patterns with very small lead pitches will be critical to the success of future VLSI packaging technologies. It is becoming increasingly important.

Current thick film multilayer ceramic (MLC) technology has reached its limits. Because silk
This is because screening techniques cannot form patterns with line widths smaller than 3 mils (0.0762 mm) and the sintering process suffers from large dimensional errors. thick film
MCL technology itself is insufficient to meet the requirements of advanced VLSI packaging technology.

One method for providing chip-to-chip and I/O interconnections is to use a thin film polyimide package on top of a conventional MLC substrate. This structure consists of an MLC substrate as a substrate for supplying current and providing mechanical support, and a thin film processed on the MLC substrate to provide chip-to-chip interconnections and to fan out semiconductor chip contacts to the thin film interconnect layer. It consists of layers. After testing various materials, it has been found that the use of polyimide as a low dielectric constant insulating layer between finely patterned high conductivity copper layers achieves the best performance.

However, a problem with using copper for microinterconnects is that the adhesion of pure copper to polyimide is not sufficient to withstand subsequent processing. Therefore, there is a need for techniques to enhance adhesion between copper and polyimide substrates.

C Problems to be Solved by the Invention It is an object of the invention to provide a multilayer thin film metallage for improving the adhesion of copper to polyimide layers.

Another object of the invention is to provide a thin film metallage for joining copper layers to ceramic layers.

Yet another object of the invention is to provide an integrated circuit package that includes a ceramic substrate and a plurality of thin film metal layers separated by polyimide dielectric layers.

D Means for Solving the Problem According to the invention, a thin film of zirconium is used as an adhesive layer between the polyimide layer and the copper layer. The bond strength between zirconium and polyimide is superior to other adhesive layers such as chromium and titanium.
Additionally, with zirconium, no spatter cleaning of the polyimide surface is required. Note that zirconium and copper can also be simultaneously deposited at the beginning of film deposition.

Furthermore, for applications where polyimide is not required for packaging, zirconium can be used as a direct adhesive layer to the ceramic substrate. Following the zirconium, copper is deposited, followed by a reactive barrier layer and a wettable surface layer such as gold. This type of construction can be used for pin brazing, chip bonding, or wire connections.

E Example FIG. 1 shows a multilayer ceramic (MLC) substrate 10.
is illustrated. MLC is known as multiple thin ceramic sheets aligned and sintered to form circuit connections for semiconductor devices. Ceramic materials include alumina ceramic (Al ₂ O ₃ ) or glass in the form known as alpha cordierite.
There is a ceramic type. Contained within layer 12 of substrate 10 are electrical conductors that are used to convey electrical signals across the substrate. Some of these conductors are illustrated as vias 14, 16 and 18, which are connected to the substrate 1.
0 is used to convey signals between the top and bottom surfaces of the substrate 10 to which it is connected to other devices.

To form electrical connections with vias 14, 16, and 18, a multilayer metal structure including a thin zirconium layer exhibits excellent mechanical and electrical properties. Although the actual structure of the multilayer metallage varies depending on the type of interconnect, the use of zirconium layers is common to all structures.
For example, multilayer pad 22 used to connect pin 24 to via 18, redesign pad 28, and surface pad 31 consists of four layers. The carture pad 26 connected to vias 14 and 16 is also comprised of a three layer metal structure.

Also shown in FIG. 1 are polyimide layers 36, 37, 3
A three-layer polyimide structure consisting of 8 is shown.
This polyimide structure is used for redistribution, chip-to-chip connections 27, and interconnections between substrate 10 and semiconductor chips 34. Furthermore, the connections within the polyimide layer are
It can also be used to directly connect one semiconductor chip to another.

Four-Layer Metallurgy For metal pads to be brazed or soldered for circuit interconnection, a four-layer structure consisting of a zirconium connection layer, a copper layer, a reactive barrier layer, and a wettable layer is preferred. Examples of pads of the type that require a four-layer structure are pad 22 to which pins 24 are brazed, redesign pads 28, and surface pads 31 to which solder balls 34 on semiconductor chips 34 are connected.

Referring to FIG. 2, the pad metallization sequence begins by aligning a mask (not shown) with a substrate 40, which may be ceramic, organic, or metallic. The type of mask used can be metal or plastic.
Any commonly used type, whether polymer or photoresist, is not critical to the invention and may be used. If polyimide is not used as the dielectric layer, a multilayer thin film pad 4
The formation of 2 begins with the deposition of a thin layer of zirconium 44. Zirconium 44 can be deposited using electron gun evaporation, sputtering, ion plating or other known techniques.
The thickness of zirconium layer 44 is preferably in the range of 30 to 2000 Angstroms.

Next, a layer 46 of copper, aluminum or gold
Deposited using the same mask deposition technique. layer 4
6 can also be deposited using the deposition techniques described above, and its preferred thickness is in the range 2-20 μm.

A thickness of 0.5 to 3.0 microns to prevent layer 46 from reacting with solder or wax during subsequent manufacturing processing.
A reaction/diffusion barrier layer 48 in the range m is deposited. This reaction barrier layer consists of zirconium, titanium,
Chromium, cobalt, tungsten, molybdenum or nickel.

Finally, a wettable surface 50 is applied to enhance the solder or braze wetting of the multilayer film. Gold in the range of 0.3 to 10 μm thick has been found effective for this purpose.

If polyimide layers are used in multilayer metallurgy, the process described above is modified to include additional steps. Referring to FIG. 3, the substrate 60
It is shown. Substrate 60 may be ceramic or may be a predeposited layer of polyimide. Layer 62 of polyimide is sprayed or spin coated to a thickness of approximately 5.0 μm.
This layer is followed by a second layer of soluble polyimide.
A layer 64 of is deposited. Layer 64 will be used as a lift-off layer after metal deposition.

A layer of photoresist 66 is then deposited and dried, and the metallization pattern is lithographically defined and developed. By using this developed photoresist pattern as an etch mask, layers 64 and 62 are
etched in a reactive ion etching chamber using O ₂ or O ₂ /CF ₄ gas mixture;
A via 68 is formed. A metal layer is then deposited in the manner described above. Lift off the board 60
This is achieved by soaking the soluble polyimide 64 in a solvent, such as n-methylpyrrolidone (NMP), which can dissolve the soluble polyimide 64.

If the metallage is to cover part of a previously deposited metal layer, the surface should be It will be necessary to clean the spatter.

This same process can be repeated as many times as necessary to form a multilayer interconnect structure as shown in FIG.

For metal pads or lines that are not exposed to the stress of brazing or soldering, such as 3-layer metallage capture pad 26, the process described above is followed with the following differences. That is, (1) the reaction barrier layer does not need to be very thick (30-2000 angstroms is sufficient), and (2) a wettable surface layer is not required. Other processing steps are the same.

F Effects of the Invention As explained above, according to the present invention, zirconium can be interposed as an adhesive layer between an insulator such as ceramic or polyimide and a metal layer such as copper to be placed on the insulator. This provides the effect of increasing the adhesion between the metal layer and the insulator.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a multilayer ceramic structure with a multilayer polyimide structure, FIG. 2 is a sectional view of a four-layer metallage, and FIG. 3 is a sectional view of a substrate with a polyimide layer and a metal structure. 44...Zirconium layer.

Claims (1)

Claims: 1. (a) a layer of zirconium deposited on a substrate; (b) a layer of a metal selected from the group of aluminum and copper deposited on said zirconium layer; (c) a layer of metal selected from the group of aluminum and copper; A multilayer metal structure comprising a reactive barrier layer selected from the group of zirconium, titanium, chromium, cobalt, tungsten, molybdenum and nickel deposited on a layer of metal.